CSS border-radius property is ignored

I am having trouble with my web application being viewed in QtWebkit.
When I specify a percent value for the css border-radius propery, eg @border-radius: 5%@ or even @-webkit-border-radius: 5%@ it is completely ignored and I get a square without rounded corners. If I specify a px value, it works fine. Everything is fine in Google Chrome / Chromium which also uses Webkit, so I don't know what is wrong with QtWebkit. Maybe it uses a different version of Webkit. I tried to report this in the qt bug tracker, but the bug form wasn't accepted, claiming it's not specific to QtWebkit (I have no idea how it would have detected that) and I should report it in Apple Webkit's bug tracker, but I know it works in Webkit, because it works in Chrome.